The present invention relates to a data detecting apparatus and its method for reproducing data recorded in recording media, and detecting data from the reproduced signal, and more particularly to a method and apparatus for realizing always a low error rate.
Recently, the recording density of recording devices such as hard disk and magnetic tape is becoming higher, and their recording capacity is increasing. In order to decode the data detected from these magnetic recording devices at low error rate, the detecting apparatus is designed to equalize the reproduced signal by partial response, and then decode at maximum likelihood by a Viterbi decoder or the like to detect data. This equalizing technology is known as partial response maximum likelihood (PRML) method. Generally two PRML methods are known well, and have been employed in magnetic recording devices. One is the partial response class 4 maximum likelihood (PR4ML) method, which equalizes and decodes the reproduced signal at maximum likelihood, so that the intersymbol interference may be [1, 0, xe2x88x921]. Other is the extended partial response class 4 maximum likelihood (EPR4ML), which equalizes and decode the reproduced signal at maximum likelihood, so that the intersymbol interference may be [1, 1, xe2x88x921, xe2x88x921].
The error rate of the data decoded by the PR4ML or EPR4ML system depends on the frequency components of signal and noise included in the reproduced signal. Generally, the PR4ML method can lower the error rate when the linear recording density is relatively low, and the EPR4ML method can lower the error rate when the linear recording density is relatively high.
Based on such fact, in the case of a conventional hard disk device, as disclosed in Japanese Patent Publication No. 2718424 and Japanese Laid-open Patent No. 8-293164, the EPR4ML and PR4ML methods are changed over, so that EPR4ML is applied in the inner circumference having high linear recording density and PR4ML is applied in the outer circumference having low linear recording density.
Japanese Patent Publication No. 2718424 discloses a magnetic disk reproducing device in which the data detector by the PR4ML system and the data detected by the EPR4ML system are changed over between the outer circumference and inner circumference of the disk, but teaches nothing about the specific method and specific configuration.
Japanese Laid-open Patent No. 8-293164 teaches to select either the PR4ML method or the EPR4ML method according to the position information of the disk registered preliminarily in the magnetic disk reproducing device, in other words, depending on the cylinder address.
Actually, however, it depends on the frequency components of signal and noise included in the reproduced signal which one of the PR4ML or EPR4ML can detect data at lower error rate. These frequency components vary significantly depending not only on the linear recording density of the recording media, but also on fluctuations of characteristics of recording media and magnetic head, time-course changes of characteristics of recording media and magnetic head, variation of spacing distance between the recording media and magnetic head, and scanning performance of magnetic head on the recording media. It is, therefore, impossible to realize the optimum low error rate always at the time of reproduction by the conventional detecting method depending only on the position information of the recording media corresponding to the linear recording density.
In particular, even in the magnetic tape recording and reproducing device having a constant linear recording density, frequency components of signal and noise included in the reproduced signal are always varying, owing to fluctuations of characteristics of magnetic tape and magnetic head, time-course changes of characteristics of magnetic tape and magnetic head, variation of spacing distance between the recording media and magnetic head, instability of contact and scanning of magnetic head on the magnetic tape, and difference in the case when reproducing a tape recorded by other magnetic tape recording device, that is, at the time of exchanging the reproducing devices. Therefore, in the magnetic tape recording and reproducing device, the best equalizing and decoding method to be applied among PR4ML or and EPR4ML is changing every moment. Moreover, in the conventional magnetic disk device, of course, it is not sufficient that the detecting method is selected based only on the linear recording density determined by the position of the disk.
It is hence an object of the invention to present a data detecting apparatus and its method capable of detecting data always at low error rate, by automatically selecting the best method among PR4ML method and EPR4ML method every moment depending on the state of reproduced signal, without referring to the position information on the disk corresponding to the predetermined linear recording density.
It is another object of the invention to present a data detecting apparatus and its method capable of automatically saving power consumption without interrupting data at the time of selection of optimum method among the PR4ML method and the EPR4ML method depending on the condition of the reproduced signal.
To achieve these objects, the data detecting method of the invention monitors the state of the reproduced signal in real time, discriminates the state of signal and noise in the reproduced signal, generates a condition discriminating signal, and automatically selects the best or optimum method among PR4ML and EPR4ML method every moment according to this condition discriminating signal.
Therefore, the data detecting method of the invention selects the best or optimum method among the PR4ML method and EPR4ML method depending on the condition of the reproduced signal itself in real time, so that it always realizes most preferable data detection method having low error rate.
Moreover, the data detecting method of the invention controls, at different timing, the operations of first decoding, second decoding and selection of system depending on the condition discriminating signal, respectively, so as hence to reduce power consumption in first decoding and second decoding operations.
Therefore, the data detecting method of the invention automatically selects the most preferable data decoding method having low error rate out of PR4ML and EPR4ML methods, every moment depending on the condition of the reproduced signal itself, at low power consumption without interrupting the data.